1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device and a method of manufacturing the device, more particularly, to a semiconductor integrated circuit device having memory cells and a method of manufacturing the device.
2. Description of the Related Art
The memory size of a static random access memory (SRAM) is smaller than that of a dynamic random access memory (DRAM). However, the processing speed of SRAMs is faster than that of DRAMs. For this reason, SRAMs have been widely used in cache memories of computers or portable appliances that require high processing speed.
Static memory cells can be classified into thin film transistor (TFT) cells, full complementary metal oxide semiconductor (FCMOS) cells, etc. An FCMOS cell may include multiple pull-up transistors and pull-down transistors, which may form a latch, and multiple pass transistors may be used to access to the latch.
However, as the integration density of semiconductor memory elements has increased, the size of memory cells has become reduced and stable operation of the memory cells has become more important.
Also, as the static noise margin (SNM) increases, the stability of memory cells may improve. In addition, as the cell ratio increases, the static noise margin may increase. As a result, there is a requirement for new technologies that may produce stable memory cells having reduced size.